Air Quality Index

EPA’s Air Quality Index (AQI)

What is EPA’s Air Quality Index?

The Air Quality Index (AQI) is a national uniform system, defined and used by the EPA, to report pollution levels for the criteria air pollutants regulated under the Clean Air Act. The AQI provides citizens with information about the general health effects associated with different pollution levels.

In Benton County, particulate air pollutants are monitored. To learn more about these pollutants and federal air quality standards for each, click here.

The AQI converts the highest measured pollutant concentration in a community’s air to a number on a scale of 0 to 500. The data is reported as a rolling 24-hour value which is updated hourly and reported here.

Washington’s Air Quality Advisory (WAQA)

What is the Washington Air Quality Advisory (WAQA)?

WAQA is very similar to the Environmental Protection Agency’s (EPA’s) national information tool, the Air Quality Index (AQI). Both use color-coded categories to show when air quality is good, moderate or unhealthy. The difference is that WAQA shows the health effects of PM2.5 at lower levels than the AQI does. In other words, WAQA shows that air quality is unhealthy earlier – when there is less PM2.5 in the air. Some examples ofPM2.5 are smoke and dust.

BCAA uses the Washington Air Quality Index to communicate information about public health. Ecology’s publication about the WAQA is here.

Since EPA already has the AQI, why did Ecology develop Washingon Air Quality Advisory?

Ecology believes WAQA better protects public health. There is new information about health risks from PM2.5. Studies show that levels of PM2.5 in the air that we previously thought were safe can cause illness and death. In fact, studies have not been able to identify any level of PM2.5 that is completely safe – that is, that has no health effects at all.

As a result of this new information, EPA changed its health standard so that air quality is now considered unhealthy when there is less PM2.5 in the air. However, EPA has not yet changed the AQI to tell people about the new information on PM2.5 health risks. EPA does not expect to update the AQI for some time. In the meantime, the AQI is not showing accurate information about health risks.

Ecology developed WAQA to tell people that PM2.5 can affect their health at lower levels than the AQI shows.

How did Ecology decide on the air quality levels in WAQA?

Ecology looked at many health studies, considered recommendations from EPA staff and EPA’s Clean Air Scientific Advisory Committee, and examined Canada’s PM2.5 standards. Based on this information, Ecology set a goal to keep PM2.5 24-hour concentrations below 20 micrograms per cubic meter of air. The pollution levels in WAQA’s color-coded categories are based on this Ecology goal, the new federal PM2.5 standard, and recommendations from scientific and health professionals.

WAQA looks very similar to the AQI. How is it different?

WAQA looks the same as the AQI because it uses the same color-coded air quality categories. Only the breakpoints for these categories are different.
The following table shows WAQA’s breakpoints on the left and AQI’s on the right. The numbers are micrograms per cubic meter of air.

As you can see from this table, when air quality is good, WAQA and AQI are either the same or very similar. But when air pollution levels begin to rise, WAQA shows air quality becoming unhealthy sooner than AQI does. Ecology believes this provides more accurate information about air pollution to the public so that those who are at risk can take action to better protect their health.

How does unhealthy air affect people?

Fine particulate matter is a major air pollutant that has been shown to cause a number of health symptoms and complications. People will have difficulties breathing polluted air depending on their age and their health. People most sensitive to air pollution include:

Infants and children

Older adults (those 65 and older)

People with lung and heart disease, stroke, diabetes, or those with a current respiratory infection.

People sensitive to air pollution may experience problems sooner and at lower levels of pollution. When people are active they breathe more air into their bodies. If air pollution levels rise, they will take in more pollutants. The amount of outdoor activity that may cause difficulties for people will be different. For example, when air pollution levels rise, daily activities such as walking the dog may cause problems for some people. Others may not be affected until doing more strenuous activity such as running. People should limit outdoor activity depending on how air quality affects them.